Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Porous graphene is considered to be a desirable membrane for gas separation. Theoretical and experimental studies indicate that atom-scale holes in the graphene lattice may provide significant selectivity for separating gases based on molecular size. Further, monolayer graphene, at one atom thick, is a desirable candidate because the gas permeation rate through a membrane increases with decreasing membrane thickness.
Porous graphene may be imagined as a rigid two-dimensional sieve, with molecule-sized pores. Molecules small enough to transit the pores may cross the membrane, whereas larger molecules may be unable to cross the membrane. Beyond size, two other mechanisms have been proposed to describe the travel of molecules through such membranes. First, in the gas phase, molecules which are small enough to actually pass through the membrane may still be restricted by statistics if they are not sufficiently aligned with a pore in terms of molecular orientation, momentum, direction of travel, etc. Second, at the graphene surface, a gas may absorb onto the graphene membrane itself, and may travel by diffusion across the surface to a pore.
All things being equal, the second mechanism could have advantages over the first mechanism since adsorbing the gas removes many degrees of freedom and removes the statistics of alignment with the pores as a factor. However, gas sorption onto a graphene surface is weak, especially at high temperatures. Thus, sorption to the graphene may not be accessible for many potentially useful applications, such as purification of hydrogen produced from water, or purification of hydrogen from the flue gas of coal plants, both of which may experience increased efficiency when conducted at high temperatures.
The present disclosure appreciates that facilitating molecular flux through porous graphene, e.g., for use in separation membranes, may be a complex undertaking.